unvented sealed central heating system

A central heating system using a boiler that (as opposed to open or vented
systems) feeds directly from the mains water supply and is supplied as a
packaged unit comprising all the necessary controls and safety devices.
A mains pressure unvented domestic hot water cylinder is used and so all
tanks/pipework are eliminated from the loft. The whole heating system is
completely sealed (i.e. unvented), which removes the risk of freezing pipes
in the loft, does away with maintenance work in the loft, and reduces the
risk of system leakage. Unvented sealed system boilers benefit the end user
with increased flow rate on their domestic hot water to all outlets in the
property as it is held at mains pressure.